void DirectionalLight(in int i, in vec3 normal,
		inout vec4 ambient, inout vec4 diffuse, inout vec4 specular)
{
	float nDotVP;	// normal . light direction
	float nDotHV;	// normal . half vector
	float pf;		// power factor
	
	nDotVP = max(0.0, dot(normal, normalize(vec3(gl_LightSource[i].position))));
	nDotHV = max(0.0, dot(normal, vec3(gl_LightSource[i].halfVector)));
	
	if( nDotVP == 0.0)
		pf = 0.0;
	else
		pf = pow(nDotHV, gl_FrontMaterial.shininess);
	
	ambient		+= gl_LightSource[i].ambient;
	diffuse		+= gl_LightSource[i].diffuse * nDotVP;
	specular	+= gl_LightSource[i].specular * pf;
}
